This invention relates generally to an apparatus and method to detect the identity and concentration of substances in recyclable materials.
The detection of various substances such as water, butane from butane lighters, heavy metals and fertilizers in bulk volumes to be recycled, such as sows, has significant safety and economic significance. Sows are rectangular blocks of scrap aluminum weighing about 1,500-lb. each. Sows and scrap bales are commonly assembled in the aluminum recycling industry, sows being normally formed from a plurality of bales or refined metals. The presence of such substances even in relatively low concentrations can result in violent explosions when the bulk volumes to be recycled are loaded into melting furnaces during a typical recycling process. For example, if the water content exceeds a certain level or if significant levels of oxidizers are present, such as can be provided by butane from butane lighters and ammonium nitrate from fertilizers, catastrophic explosions can result.
Current empirically-derived practices for detecting such substances involve preheating sows for extended periods of time to evaporate an unknown quantities of water and other substances contained within the sow. For example, a typical preheating step can be performed for 6 hours at 700xc2x0 F. This practice is time-consuming, energy intensive and dependent on closely following stringent operational guidelines derived from empirical experience. The amount of energy consumed for preheating aluminum sows alone is approximately equal to the amount of energy it takes to melt the aluminum sows. Furthermore, investments in and maintenance of preheat furnaces are required to support the moisture evaporation step used in conventional aluminum recycling processes.
Because the moisture level is not measured in conventional aluminum recycling, a preheating step is generally required to remove moisture, whether the moisture level entrapped in the so-called shrinkage cavities of sows is above or below a safe level. This results in the performance of a preheating step in instances when the preheating step may be unnecessary. Preheating practices followed are conservative and result in significant economic costs. Typical shrinkage cavities in 1,500-lb sows can accumulate volumes of water, from sources such as rainfall, in amounts typically from approximately 0.25 to 1.25 gallons (about 1 to 4 liters) per sow.
The existence of contaminating substances, such as lead, in scrap bales can also completely void the quality of the finished product. Accordingly, it is also important to detect and remove these substances, prior to bales being charged into furnaces. Current practice involves manually searching through selected bales to identify certain contaminating substances prior to charging furnaces.
X-rays are generally not useful as applied to contamination detection in bulk volumes, and accordingly are not used for this purpose. X-rays can be used to produce sharp images as well as density-dependant shading of interrogated objects. However, X-rays primarily provide information relating to the bulk properties of an object, and cannot provide substance-specific information. As a result, the application of an X-ray system to a sow to detect moisture cannot determine whether a density difference detected is due to an empty cavity, a cavity filled with water, some potentially explosive compound, or some other cause. Ultrasound techniques, which can be useful when used for crack or flaw detection, cannot be used for contaminant detection because ultrasound typically generates considerable scattering-induced noise and is also incapable of identifying specific substances.
Methods are used between the melt and casting steps to detect and remove hydrogen and unwanted inclusions, the inclusions being mainly oxides of elements such as magnesium and aluminum. The current practice typically used for detecting hydrogen involves use of the so-called Alscan probe, which is based on monitoring the thermal conductivity of a xe2x80x9csippedxe2x80x9d sample drawn from a bulk material. For inclusion detection, a Limca probe is utilized which also uses small samples and detects inclusions via, monitoring electrical resistance changes from sipped samples. These techniques are both intrusive techniques which monitor small samples, require expensive equipment and cannot identify specific substances. Thus, current techniques do not provide the ability to assess bulk volumes of material, cannot detect contaminants with specificity, and cannot locate the position of contaminants within a given bulk volume.
A neutron detection system for detection of contaminants contained within a bulk material during recycling includes at least one neutron generator for neutron bombardment of a bulk material. At least one gamma ray detector is provided for detection of gamma rays emitted by contaminants within the bulk material responsive to the neutron bombardment. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of at least one contaminant in the bulk material.
The system can include a neutron reflector for reflecting at least a portion of neutrons which pass through the bulk material back into the bulk material, the neutron reflector disposed on an end of the bulk material distal to an end of the bulk material which receives an initially incident neutron beam emitted from the neutron generator. The neutron reflector can be made from Be, beryllium oxide and graphite. The system can include a structure for scanning a neutron beam emitted from the neutron generator across a portion of the bulk material to identify portions of the bulk material having contaminants. Discrete locations having contaminants can be identified with a 2-dimensional, or more preferably, with a 3-dimensional description.
The system can include a structure for removing detected contaminants from the bulk material. The structure for removing contaminants can be adapted to direct an energetic beam at discrete locations of the bulk material found to have contaminants. The structure for removing contaminants can be selected from a microwave source, an infrared and an acoustical source. Preferably, the structure for removing contaminants is an ultrasonic source, provided the contaminants are fluid contaminants.
The system can comprise at least two neutron generators, the neutron generators emitting at least two distinct neutron energy spectrums. The first neutron generator can emit neutrons having average energies of least 6 MeV and a second neutron generator can emit neutrons having average energies less than the first neutron generator. The first neutron generator can be a deuterium-tritium (D-T) generator and the second neutron generator can be a deuteriumxe2x80x94deuterium (Dxe2x80x94D) generator or an isotopic generator.
The bulk material for recycling can be scrap aluminum. The aluminum can be in the form of at least one sow. The structure for analyzing gamma ray data can be adapted to determine the identity, concentration and locations of contaminants in the bulk material.
A neutron detection system includes at least one neutron generator for neutron bombardment of a material, at least one gamma ray detector for detection of gamma rays emitted by the material responsive to the neutron bombardment, and a neutron reflector for reflecting at least a portion of the neutrons which pass through the material back into the material. The neutron reflector is disposed on an end of the material distal to an end of the material which receives an initially incident neutron beam emitted from the neutron generator. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of at least one substance in the material.
In another embodiment of the invention, a neutron detection system includes at least two neutron generators, the neutron generators emitting at least two distinct neutron energy spectrums for neutron bombardment of a material. At least one gamma ray detector is provided for detection of gamma rays emitted from the material responsive to the neutron bombardment, and a structure for analyzing gamma ray data communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of at least one substance in the material.
In another embodiment of the invention, a neutron detection system includes at least one neutron generator for neutron bombardment of a material, and at least one gamma ray detector for detection of gamma rays emitted by the material responsive to the neutron bombardment. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of at least one contaminant in the material. A structure for scanning a neutron beam emitted from the neutron generator across a portion of the material is provided to enable identifying portions of the material having contaminants. The system can include a structure for reducing the concentration of contaminants found in the locations having contaminants without substantially altering a composition of the material.
A method for recycling bulk material having unknown levels of contaminants includes the steps of providing at least one neutron generator for neutron bombardment of a bulk material and at least one gamma ray detector for detection of gamma rays emitted by contaminants within the bulk material responsive to the neutron bombardment. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of at least one contaminant in the bulk material. The bulk material is irradiated with emitted neutrons, and the presence of contaminants in the bulk material is determined from gamma rays emitted from the bulk material. The method can include the step of melting the bulk material without treatment to remove the contaminants, provided the determined concentration of contaminants are below predetermined limits.
The bulk material can be aluminum. In the case of bulk aluminum, the method can include the step of melting the bulk aluminum without treatment to remove the contaminants, such as water, provided the determined concentrations of the contaminants are below predetermined limits.
The method can include the step of reflecting at least a portion of the neutrons which pass through the bulk material back into the bulk material. The method can also include the step of scanning a neutron beam emitted by the neutron generator across a portion of the bulk material, the scanning identify portions of the bulk material having contaminants. The locations having contaminants can be represented in 2-dimensions, or more preferably, in 3-dimensions.
The method can include the step of determining at least one of the identity, concentration and location of contaminants in the bulk material. Contaminants can be removed by directing energy emitted from an acoustical source onto discrete locations of the bulk material found to have contaminants. Acoustical removal is particularly attractive when contaminants are fluids.
At least two neutron generators can be provided, the generators emitting at least two distinct neutron energy spectrums. The generators can include a first neutron generator emitting neutrons having energies of at least 6 MeV and a second neutron generator emitting neutrons having a lower average energy than the first neutron generator. The second generator can be a Dxe2x80x94D generator or an isotopic generator. The method can include the step of moderating neutrons emitted by the second generator prior to irradiating the bulk material. The bulk material can be at least one sow.
In another embodiment of the invention, a method of moisture detection includes the steps of providing at least one neutron generator for neutron bombardment of a material, and at least one gamma ray detector for detection of gamma rays emitted by the material responsive to the neutron bombardment. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector, the structure for analyzing gamma ray data adapted to determine the presence of water if present in the material. The material is irradiated with emitted neutrons. The presence and concentration of water in the material is determined from gamma rays emitted from the material. The method can include the step of identifying portions of the material having water. Preferably, the identifying step includes representing locations found having water in 2-dimensions, or more preferably, in 3-dimensions.
In yet another embodiment of the invention, a method for identifying discrete locations of contaminants within a bulk material includes the steps of providing at least one neutron generator for neutron bombardment of bulk material, and at least one gamma ray detector for detection of gamma rays emitted by contaminants within the bulk material. A structure for analyzing gamma ray data is communicably connected to the gamma ray detector is provided, the structure for analyzing gamma ray data adapted to determine the presence of at least one contaminant in the bulk material. A first portion of the bulk material is irradiated with emitted neutrons and the presence and concentration of contaminants in the first portion are determined from gamma rays emitted from the first portion. The neutron generator is moved to permit irradiation of another portion of the bulk material, the other portion different from the first portion. The other portion is irradiated with neutrons and the presence and concentration of contaminants in the other portion is determined from gamma rays emitted from the other portion.
The first portion can be substantially the entire bulk material, the other portion being a portion less than the entire bulk material. The method can include the step of scanning at least one of the neutron generators across a surface of the bulk material, where a plurality of portions of the bulk material can be tested.